This invention relates to a water vapor permeable, pressure sensitive adhesive composition with enhanced water vapor transmission and which is useful in preventing skin damage by excess water sweat in skin contact applications such as medical and surgical dressing tapes.
During the last several years, there has been much activity in developing pressure sensitive adhesives in water or moisture vapor permeable wound dressings, bandages, and drapes for use in the medical field. It has been found that these moisture vapor permeable, pressure sensitive adhesive dressings provide an improved surgical covering or bandage which speeds the natural wound healing process, while also protecting the wound site. In general, the wound dressings, bandages and surgical drapes allow water vapor to escape from a wound site while preventing liquid water from either entering or escaping from the site. In addition, bacteria is also prevented from passing through the wound dressing, thereby protecting the wound site from bacterial invasion.
Typically, these wound dressings, bandages, and surgical drapes all comprise a membrane layer which incorporates the desired physical characteristics to attain the moisture vapor permeability while preventing liquid water and bacteria from passing through the membrane. In addition, one surface of the membrane incorporates an adhesive which provides the desired pressure sensitive adherence for securing the membrane to the wound site and retaining the membrane in the desired position.
Moisture vapor permeable, pressure sensitive adhesive membranes are typically applied to a patient as a flat sheet, ranging in size from a few square inches to one or two square feet. In order to achieve the desired results, these moisture vapor permeable, pressure sensitive adhesive membranes are extremely thin and pliable. In this way, the desired permeability is provided, and membranes are able to conform to the shape of the patient's body or skin.
Moisture vapor permeable thin films coated with adhesive and which are suitable for application to the skin have been disclosed, for example, in British Patent No. 1,280,631 and in U.S. Pat. No. 3,645,835, as well as European Patent Application Nos. 51935, 81987, 117632 and 178740 and U.S. Pat. Nos. 4,372,303, 4,374,520 and 4,413,621. The known dressings of this type in commercial use have proved useful because the microscopically continuous nature of the adhesive layer and the film prevents ingress of bacteria into the wound.
These dressings have the added advantage that they do not cause maceration of healthy skin to which they may be applied because both the film and the adhesive layer are moisture vapor permeable and generally provide the dressing with a moisture vapor transmission rate (MVTR) of between 300 and 800 g/m.sup.2 /24 hr. at 37.degree. C. and 100% to 10% relative humidity difference.
However, disadvantages which may arise with known incise drapes include the possibility that if the patient sweats profusely, the adhesive may be affected and the drape may lift away from the skin and thereby compromise the sterility of the operation site.
Similarly with commercially available intravenous access site dressings (I.V. dressings), although the adhesives employed are moisture vapor permeable, the moisture vapor transmission rate (MVTR) of the adhesive when present as a continuous film is not sufficiently high to permit rapid evaporation of moisture through a dressing which has been applied to an exuding site. The result of using such an adhesive can cause the formation of a moist area which can predispose the area to bacterial growth.
Thin film dressings known for use as wound dressings also suffer from the disadvantage that the MVTR of the moisture vapor permeable adhesive when present as a continuous film is not sufficiently high to permit rapid evaporation of moisture from a dressing which has been applied to an exuding wound. The result of using such an adhesive can cause the formation of an unsightly blister which can predispose the area to leakage and lead to bacterial contamination.
One method of overcoming the disadvantages associated with known thin film dressings is to provide the adhesive layer as a macroscopically discontinuous layer in the form of a porous or a pattern spread layer as disclosed in European Patent No. 91800. Such a layer is coated onto a continuous moisture vapor permeable or water absorbent backing layer so that the dressing remains bacteria-proof while also possessing a high moisture vapor transmission rate. However, the discontinuous nature of the adhesive layer can give rise to other disadvantages. The edges of the dressing may lift at the adhesive free areas. The discontinuous adhesive layer may allow exudate, such as in the case of wound or IV dressings, to spread away from the wound or access site over the skin which may cause trauma to the skin. The exudate may ultimately reach the edge of the dressing thereby providing a possible route by which bacteria might reach the wound or site. A discontinuous adhesive layer may allow local drying out of the wound and hence lead to scab formation. None of these occurrences are conducive to wound healing and may lead to a traumatic removal of the dressing.
It would be advantageous therefore if a dressing could be provided with an adhesive present as a continuous layer whereby the above disadvantages of grossly discontinuous adhesive layers can be avoided. It would also be advantageous if the dressing had a greater moisture vapor transmission rate. A dressing of this type is disclosed in WO 88/01877 and involves a thin film adhesive dressing comprising a support layer having a continuous coating on one side of a gel adhesive which is not self adherent and which is a hydrophilic gel containing polyurethane residue.
For many years, the pressure sensitive adhesives that have been used for attachment of these dressing materials to the skin surface were natural rubber based, and therefore they contained the usual chemical additives, such as resins, plasticizers, anti-oxidants, etc. The foregoing listed chemical additives, in addition to others, are potentially irritating to human skin. In addition, as the pressure sensitive adhesive and, in some cases, the dressing materials were occlusive and water vapor non-permeable by nature, the adhesive sheet materials led to water accumulation thereunder. The accumulated water would then over hydrate and soften the outer layers of the skin (stratum corneum) thus causing what is referred to as skin maceration. Additionally, the stratum corneum of the macerated skin is easily further damaged when the pressure sensitive adhesive coated sheet material is removed. Therefore, in order to prevent the widely prevalent moisture caused maceration of skin, the pressure sensitive adhesive coated sheet materials should preferably be composed of water vapor permeable adhesive substrate backings and non-irritating pressure sensitive adhesives.
Many of the modern surgical adhesive dressings and bandages employ an acrylic based pressure sensitive adhesive, which is much more permeable to water than the prior art rubber based occlusive adhesive compositions. Although acrylic based pressure sensitive adhesives are less traumatic to human skin than those which are rubber based, they are not without their inherent disadvantages. Especially in applications where the pressure sensitive adhesive coated dressing sheet material is repeatedly applied to and then removed from the same area of the skin surface, e.g., as in the changing of a medical or surgical dressing, or when in place over a prolonged period of time, a significant local skin damage or water induced maceration can result.
Conventional acrylic-based pressure sensitive adhesive compositions are generally single component materials, comprised of copolymers of alkyl acrylate (C.sub.1 -C.sub.12) esters with polar monomers such as acrylic acid, acrylonitrile, acrylamide, etc. Optional modifying monomers which may also be copolymerized with alkyl acrylate esters are methyl or ethyl acrylate, alkyl (C.sub.1 -C.sub.8) methacrylates, styrene, vinyl acetate, etc.
British Patent No. 2,070,631A to R. F. Peck, teaches the copolymerization of n-butyl acrylate, 2-ethylhexyl acrylate and acrylic acid to produce a polyacrylate having a K-value of from 90 to 110 claimed to result in a satisfactory water vapor permeability for use with medical dressings.
E. Schonfeld (U.S. Pat. No. 4,140,115) has proposed the incorporation of a polyol, such as polyoxyalkylene glycol, in the acrylic adhesive mass for use in surgical and/or medical bandages or tapes, which are claimed to result in less skin damage upon their removal.
Ono, et al., (U.S. Pat. No. 3,975,570) has proposed to improve the water vapor permeability of conventional acrylic pressure sensitive adhesives by blending therewith hydroxyethyl cellulose.
K. R. Shah (U.S. Pat. No. 4,337,325) has described blending alkyl acrylic acid copolymers with certain proportions of N-vinyl lactam homopolymers and copolymers to obtain pressure sensitive adhesives having increased water vapor permeabilities.
H. Reinhard, et al. (U.S. Pat. No. 3,725,122), discloses a pressure sensitive adhesive comprising a copolymer of primary and/or secondary alkyl acrylate (C.sub.4 -C.sub.12) esters, of which at least 25 percent are derived from alkanols having 6 to 12 carbon atoms, tertiary alkyl (C.sub.4 -C.sub.12) esters, N-vinyl pyrrolidone (1 to 10 percent by weight), and olefincally unsaturated monomers (such as acrylic acid, acrylamide, etc.) containing reactive groups.
U.S. Pat. No. 4,181,752 to Martens, et al., discloses a process for the free radical polymerization of acrylic monomers by means of ultraviolet irradiation under controlled conditions in order to prepare pressure sensitive adhesives. N-vinyl pyrrolidone and acrylic acid have been mentioned as monomers copolymerizable with alkyl acrylates by the irradiation process.
A water vapor permeable, pressure sensitive adhesive composition useful for surgical and medical bandage applications is disclosed in U.S. Pat. No. 4,510,197 to K. Shah and comprises copolymers of butyl acrylate, N-vinyl-2-pyrrolidone and acrylic acid.
European Patent Application 194,881 discloses emulsion polyacrylate adhesive polymers which are useful as surgical and medical dressings. The polymer compositions contain a copolymerizable sulfonate surfactant to form a stable, water insensitive emulsion and further comprise acrylic residues of alkyl esters of acrylic or methacrylic acid and optionally may contain small amounts (0.3 to 5%) of hydroxylated alkyl esters of acrylic or methacrylic acid
While several acrylic based, water vapor permeable adhesive compositions are disclosed in the above mentioned references, there is no disclosure of an all acrylic, single polymer system free of additives having an especially enhanced water vapor transmission.